The present invention relates to an apparatus and method for providing a high volume output of monodisperse aerosols and to permit changing the particle size generated simply and conveniently. Additionally, the high volume is attainable by permitting rapid transfer of heat to atomized materials to cause droplets to form a vapor, which when passed through a condenser will cause condensation of the aerosol material onto provided seed material particles to form a desired particle size.
It is desired in industrial settings to have aerosols that contain a known particle size in a monodisperse aerosol (substantially only one particle size carried in the fluid). These aerosols are used for calibrating and testing items such as filters and other applications where trapping of particular particle sizes is of importance.
In the prior art, the generation of monodispersed aerosols using a generator that involves vaporization and subsequent condensation, is described in an article by Benjamin Y.H. Liu et al., entitled A Condensation Aerosol Generator For Producing Monodispersed Aerosols In The Size Range, 0.036.mu. To 1.3.mu., "Journal de Recherches Atmospheriques", pp. 397-406, 1966. A single generator is utilized and the formation of the aerosol is controlled so that the correct particle size is generated. The process includes vaporizing a high boiling point material by heating it, and then cooling the vapor to form the monodisperse aerosol of a standard size. Because many of the organic materials with suitable vapor pressure-temperature relationships required for particle generation will thermally decompose when coming into direct physical contact with heated surfaces at high temperatures, the Liu et al. article described a method whereby the aerosol material is first atomized to form a droplet spray, which is then heated to form the vapors. The heat is transferred to the droplets through an intervening air layer and, thus, direct contact between the aerosol material and the heated surface was avoided to avoid the material decomposition problem.
An additional problem arose with the apparatus shown in the Liu et al. article when more than one particle size was desired for running a series of experiments or for other purposes. The aerosol atomizer had to be emptied and refilled with the proper solution.
The present invention relates to improvements to the device shown in the Liu et al. article that makes it adaptable to commercial evaluations where more than one particle size is needed for testing, and which will provide for high flow rates without large physical size by providing for a compact heater and condenser.
The basic principle of use in the Liu et al. article is that the aerosol material will be atomized to form a droplet spray, which is then heated to form a vapor. The vapor is condensed in the presence of a seed material that forms nuclei for condensation. If the concentration of the aerosol material in the aerosol atomizer is maintained, the particle size in the monodisperse aerosol will be uniform.